Solid electrolyte material, lithium battery, and method of producing solid electrolyte material

ABSTRACT

A main object of the present invention is to provide a solid electrolyte material having excellent Li ion conductivity. To attain the object, the present invention provides a solid electrolyte material represented by a general formula: Li x (La 2−a M1 a )(Ti 3−b M2 b )O 9+δ , characterized in that “x” is 0&lt;x≦1; “a” is 0≦a≦2; “b” is 0≦b≦3; “δ” is −2≦δ≦2; “M1” is at least one selected from the group consisting of Sr, Na, Nd, Pr, Sm, Gd, Dy, Y, Eu, Tb, and Ba; and “M2” is at least one selected from the group consisting of Mg, W, Mn, Al, Ge, Ru, Nb, Ta, Co, Zr, Hf, Fe, Cr, and Ga.

TECHNICAL FIELD

The present invention relates to a solid electrolyte material havingexcellent Li ion conductivity.

BACKGROUND ART

In accordance with a rapid spread of information relevant apparatusesand communication apparatuses such as a personal computer, a videocamera and a portable telephone in recent years, as a power sourcethereof the development of a battery to be utilized has been emphasized.The development of a high-output and high-capacity battery for anelectric automobile or a hybrid automobile has been advanced also in theautomobile industry. A lithium battery has been presently noticed fromthe viewpoint of a high energy density among various kinds of batteries.

Liquid electrolyte containing a flammable organic solvent is used for apresently commercialized lithium battery, so that the installation of asafety device for restraining temperature rise during a short circuitand the improvement in structure and material for preventing the shortcircuit are necessary therefor. On the contrary, a lithium batteryall-solidified by replacing the liquid electrolyte with a solidelectrolyte layer is conceived to intend the simplification of thesafety device and be excellent in production cost and productivity forthe reason that the flammable organic solvent is not used in thebattery.

A Li—La—Ti—O-based solid electrolyte material (LLT) has been known as asolid electrolyte material used for an all solid state lithium battery.For example, in Patent Literature 1, a solid electrolyte membrane havinglithium ion conductivity is disclosed, which has a composition ofLa_(x)Li_(y)Ti_(z)O₃ (0.4≦X≦0.6, 0.4≦Y≦0.6, 0.8≦Z≦1.2, Y<X) and is anamorphous structure.

Further, in Patent Literature 2, a solid electrolyte layer composed of asolid electrolyte comprising a complex oxide containing Li, La and Ti isdisclosed, which has an amorphous layer, a crystalline layer and alattice defect layer. In addition, in Patent Literature 2, it isdescribed that the composition of a solid electrolyte material ispreferably La_(2/3-x)Li_(3x)TiO₃ (0.03≦x≦0.167). This solid electrolytematerial is synthesized by performing planetary ball milling andburning, and corresponds to so-called bulk body, not a thin membrane.

Further, in Patent Literature 3, a perovskite type complex oxiderepresented by Li_(x)La_(y)Ti_(z)O₃ (x, y, z satisfy 0.08≦x≦0.75,0.8≦z≦1.2, x+3y+4z=6) is disclosed. Further, in Examples of PatentLiterature 4, a lithium ion conductor represented byLi_(0.34)La_(0.51)TiO_(2.94) is disclosed. Further, in Examples ofPatent Literature 5, a perovskite type oxide represented byLi_(0.26)La_(0.57)TiO₃ is disclosed.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent Application Laid-Open (JP-A) No.2009-238704

Patent Literature 2: JP-A No. 2008-059843

Patent Literature 3: JP-A No. H11-079746

Patent Literature 4: JP-A No. H06-333577

Patent Literature 5: JP-A No. H09-219215

SUMMARY OF INVENTION Technical Problem

A solid electrolyte material having excellent Li ion conductivity hasbeen demanded from the viewpoint of achieving higher output of abattery. The present invention has been made in view of theabove-mentioned actual circumstances, and a main object thereof is toprovide a solid electrolyte material having excellent Li ionconductivity.

Solution to Problem

To attain the object, the present invention provides a solid electrolytematerial represented by a general formula:Li_(x)(La_(2−a)M1_(a))(Ti_(3−b)M2_(b))O_(9+δ), characterized in that “x”is 0<x≦1; “a” is 0≦a≦2; “b” is 0≦b≦3; “δ” is −2≦δ≦2; “M1” is at leastone selected from the group consisting of Sr, Na, Nd, Pr, Sm, Gd, Dy, Y,Eu, Tb, and Ba; and “M2” is at least one selected from the groupconsisting of Mg, W, Mn, Al, Ge, Ru, Nb, Ta, Co, Zr, Hf, Fe, Cr, and Ga.

A solid electrolyte material having excellent Li ion conductivity may beobtained for the reason that the present invention has theabove-mentioned general formula.

In the above-mentioned present invention, the above-mentioned “x” ispreferably 0.02≦x≦0.28. The reason therefor is to allow a solidelectrolyte material having more excellent Li ion conductivity.

In the above-mentioned present invention, the above-mentioned “x” ispreferably 0.09≦x≦0.24. The reason therefor is to allow a solidelectrolyte material having remarkably high Li ion conductivity.

In the above-mentioned present invention, the solid electrolyte materialis preferably a crystalline material. The reason therefor is that Li ionconductivity in a crystal grain is high. In the present invention, forexample, the use of a reactive deposition method allows crystal grainsto be favorably joined to each other and allows resistance increase in agrain boundary to be restrained even in the case of being a crystallinematerial.

In the above-mentioned present invention, the solid electrolyte materialpreferably has a perovskite structure. The reason therefor is to allow asolid electrolyte material having high Li ion conductivity.

In the above-mentioned present invention, the solid electrolyte materialis preferably in thin film form. For example, the reason therefor isthat the use of a reactive deposition method allows the minute solidelectrolyte material to be obtained and allows Li ion conductivity to beimproved.

In the above-mentioned present invention, the solid electrolyte materialpreferably has a thickness of 200 nm to 5 μm.

In the above-mentioned present invention, the “a” and the “b” arepreferably 0.

Further, the present invention provides a lithium battery comprising: acathode active material layer containing a cathode active material, ananode active material layer containing an anode active material, and asolid electrolyte layer formed between the above-mentioned cathodeactive material layer and the above-mentioned anode active materiallayer, characterized in that the above-mentioned solid electrolyte layercontains the above-mentioned solid electrolyte material.

According to the present invention, the use of the above-mentioned solidelectrolyte material allows a high-output lithium battery.

Further, the present invention provides a method of producing a solidelectrolyte material, including steps of: preparing a raw material, inwhich the raw material is made of Li, La, Ti, M1 (M1 being at least oneselected from the group consisting of Sr, Na, Nd, Pr, Sm, Gd, Dy, Y, Eu,Tb, and Ba), and M2 (M2 being at least one selected from the groupconsisting of Mg, W, Mn, Al, Ge, Ru, Nb, Ta, Co, Zr, Hf, Fe, Cr, andGa); and forming a thin film, in which the solid electrolyte material isformed using the raw material to a substrate by a reactive depositionmethod using oxygen, and the solid electrolyte material is representedby a general formula: Li_(x)(La_(2−a)M1_(a))(Ti_(3−b)M2_(b))O_(9+δ), inwhich “x” is 0<x≦1; “a” is 0≦a≦2; “b” is 0≦b≦3; “δ” is −2≦δ≦2.

According to the present invention, the use of the reactive depositionmethod allows a minute thin film to be formed, and a solid electrolytematerial having excellent Li ion conductivity may be obtained by theabove-mentioned general formula.

In the above-mentioned present invention, the above-mentioned “x” ispreferably 0.02≦x≦0.28. The reason therefor is to allow a solidelectrolyte material having more excellent Li ion conductivity.

In the above-mentioned present invention, it is preferable that theabove-mentioned solid electrolyte material is a crystalline material andhas a perovskite structure. The reason therefor is to allow a solidelectrolyte material having high Li ion conductivity.

In the above-mentioned present invention, the solid electrolyte materialpreferably has a thickness of 200 nm to 5 μm. The reason therefor isthat the minute solid electrolyte material may be obtained and Li ionconductivity may be improved.

In the above-mentioned present invention, the solid electrolyte materialis preferably formed in the thin film forming step by the reactivedeposition method using an oxygen plasma.

In the above-mentioned present invention, the substrate is preferably amember containing a cathode active material layer or an anode activematerial layer. The reason therefor is to be useful for producing alithium battery.

Advantageous Effects of Invention

The present invention produces the effect such as to allow a solidelectrolyte material having excellent Li ion conductivity.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a ternary view explaining a solid electrolyte material of thepresent invention.

FIG. 2 is a schematic cross-sectional view showing an example of alithium battery of the present invention.

FIG. 3 is a schematic cross-sectional view showing an example of amethod of producing a solid electrolyte material of the presentinvention.

FIG. 4 is a result of activation energy of a solid electrolyte materialobtained in Examples 1 to 7.

DESCRIPTION OF EMBODIMENTS

A solid electrolyte material, a lithium battery and a method ofproducing a solid electrolyte material of the present invention arehereinafter described in detail.

A. Solid Electrolyte Material

A solid electrolyte material of the present invention is firstdescribed. A solid electrolyte material of the present invention isrepresented by a general formula:Li_(x)(La_(2−a)M1_(a))(Ti_(3−b)M2_(b))O_(9+δ), characterized in that “x”is 0<x≦1; “a” is 0≦a≦2; “b” is 0≦b≦3; “δ” is −2≦δ≦2; “M1” is at leastone selected from the group consisting of Sr, Na, Nd, Pr, Sm, Gd, Dy, Y,Eu, Tb, and Ba; and “M2” is at least one selected from the groupconsisting of Mg, W, Mn, Al, Ge, Ru, Nb, Ta, Co, Zr, Hf, Fe, Cr, and Ga.

A solid electrolyte material having excellent Li ion conductivity may beobtained for the reason that the present invention has theabove-mentioned general formula. Further, as described in theafter-mentioned Examples, the determination of the specific range of “x”allows a solid electrolyte material having high Li ion conductivity (lowactivation energy).

FIG. 1 is a ternary view explaining a solid electrolyte material of thepresent invention. With regard to a solid electrolyte material of thepresent invention, as shown in the above-mentioned general formula, partor all of La and part or all of Ti may be substituted with other metals(M1, M2); yet, in FIG. 1, the case where the solid electrolyte materialis an Li—La—Ti—O-based solid electrolyte material is described forconvenience. A solid electrolyte material of the present invention has acomposition on a tie line of Li and La₂Ti₃O₉ as shown by the linesegment A in FIG. 1. On the other hand, the solid electrolyte materialdescribed in Patent Literature 1 has a composition shown by the area Bin FIG. 1 when numerical ranges of “x”, “y”, and “z” are shown in theternary view. Similarly, the solid electrolyte material described inPatent Literature 2 has a composition shown by the line segment C inFIG. 1. The composition area (the area A) in the present inventiondiffers completely from the composition areas shown by the area B andthe line segment C, and is a new composition area which has notconventionally been known. As described in the after-mentioned Examples,it was confirmed that excellent Li ion conductivity was exhibited alsoin this new composition area.

A solid electrolyte material of the present invention is represented bya general formula: Li_(x)(La_(2−a)M1_(a))(Ti_(3−b)M2_(b))O_(9+δ). In theabove-mentioned general formula, “x” is 0<x≦1. In the present invention,“x” is preferably 0.02≦x, and more preferably 0.09≦x. As described inthe after-mentioned Examples, the reason therefor is to allow a solidelectrolyte material having excellent Li ion conductivity. On the otherhand, in the present invention, ordinarily, “x” is preferably x≦0.5,more preferably x≦0.28, and far more preferably x≦0.24. The reasontherefor is to allow a solid electrolyte material having excellent Liion conductivity.

Further, in the above-mentioned general formula, “a” is 0≦a≦2, andpreferably 0≦a≦1. Similarly, in the above-mentioned general formula, “b”is 0≦b≦3, and preferably 0≦b≦1.5. In the present invention, “a” or “b”may be 0, and “a” and “b” may be 0.

Further, in the above-mentioned general formula, “δ” is −2≦δ≦2. Inconsideration of valences of metallic elements included in theabove-mentioned general formula, the above-mentioned general formula maybe denoted as Li_(x)(La_(2−a)M1_(a))(Ti_(3−b)M2_(b))O_(9+x/2) by theelectroneutrality principle; yet, oxygen depletion and oxygen excess maybe actually caused. In particular, in the case where a solid electrolytematerial of the present invention is a crystalline material, oxygendeficiency such that oxygen is lost from an oxygen lattice and oxygenexcess such that oxygen exists excessively by influence of a slightamount of an impurity phase are easily caused. Thus, in the presentinvention, the range of δ is prescribed at −2≦δ≦2 in consideration ofoxygen deficiency and oxygen excess.

Further, in the above-mentioned general formula, “M1” is a metal capableof being located at the same site as that of La in a crystal structure;specifically, at least one selected from the group consisting of Sr, Na,Nd, Pr, Sm, Gd, Dy, Y, Eu, Tb, and Ba.

Further, in the above-mentioned general formula, “M2” is a metal capableof being located at the same site as that of Ti in a crystal structure;specifically, at least one selected from the group consisting of Mg, W,Mn, Al, Ge, Ru, Nb, Ta, Co, Zr, Hf, Fe, Cr, and Ga.

A solid electrolyte material of the present invention may be amorphousor crystalline. The case of being amorphous has the advantage thatresistance increase in a grain boundary may be prevented. On the otherhand, the case of being crystalline has the advantage that Li ionconductivity in a crystal grain is high. In addition, in the presentinvention, the use of the after-mentioned reactive deposition methodallows crystal grains to be favorably joined to each other and allowsresistance increase in a grain boundary to be restrained even in thecase of being crystalline. Further, a solid electrolyte material of thepresent invention preferably has a perovskite structure. The reasontherefor is to allow a solid electrolyte material having high Li ionconductivity. In particular, a solid electrolyte material of the presentinvention is preferably a single-phase compound having a perovskitestructure. The reason therefor is to allow Li ion conductivity to bemade higher.

Further, a solid electrolyte material of the present invention may bebulky or in thin film form, and is preferably in thin film form. Thereason therefor is that the use of the after-mentioned reactivedeposition method allows a minute solid electrolyte material to beobtained and allows Li ion conductivity to be improved.

The size of a solid electrolyte material of the present invention is notparticularly limited. Above all, in the case where a solid electrolytematerial of the present invention is in thin film form, the thickness ofthe thin film is preferably 200 nm or more, more preferably 500 nm ormore, and far more preferably 800 nm or more. On the other hand, thethickness of the thin film is preferably 5 μm or less, more preferably 3μm or less, and far more preferably 2 μm or less.

Further, a solid electrolyte material of the present invention ispreferably low in activation energy of Li ion conduction. The reasontherefor is to allow a solid electrolyte material having high Li ionconductivity. The relation between Li ion conductivity and activationenergy may be represented by the following expression.σ=σ₀exp(−E/RT)

In the expression, σ is Li ion conductivity (S/cm), σ₀ is total powerterm, E is activation energy (J/mol), R is gas constant, and T isabsolute temperature (K).

As shown in the above-mentioned expression, smaller activation energy Ebrings larger Li ion conductivity σ. Activation energy may be expressedby a unit of [eV]. With regard to a solid electrolyte material of thepresent invention, activation energy is preferably 0.60 eV or less, morepreferably 0.55 eV or less, and far more preferably 0.50 eV or less.

A solid electrolyte material of the present invention may be used foroptional uses in which Li ion conductivity is required. Examples of theuses of the solid electrolyte material include batteries such as alithium battery and sensors such as a gas sensor. A method of producinga solid electrolyte material of the present invention is described indetail in the after-mentioned ‘C. Method of producing solid electrolytematerial’. A solid electrolyte material in a bulk body may be producedby using a method such as a mechanical milling method and a solid phasemethod.

B. Lithium Battery

Next, a lithium battery of the present invention is described. A lithiumbattery of the present invention is a lithium battery comprising: acathode active material layer containing a cathode active material, ananode active material layer containing an anode active material, and asolid electrolyte layer formed between the above-mentioned cathodeactive material layer and the above-mentioned anode active materiallayer, characterized in that the above-mentioned solid electrolyte layercontains the above-mentioned solid electrolyte material.

According to the present invention, the use of the above-mentioned solidelectrolyte material allows a high-output lithium battery.

FIG. 2 is a schematic cross-sectional view showing an example of alithium battery of the present invention. A lithium battery 10 in FIG. 2comprises: a cathode active material layer 1 containing a cathode activematerial, an anode active material layer 2 containing an anode activematerial, a solid electrolyte layer 3 formed between the cathode activematerial layer 1 and the anode active material layer 2, a cathodecurrent collector 4 for performing current collecting of the cathodeactive material layer 1, an anode current collector 5 for performingcurrent collecting of the anode active material layer 2, and a batterycase 6 for storing these members. The present invention is greatlycharacterized in that the solid electrolyte layer 3 contains the solidelectrolyte material described in the above-mentioned ‘A. Solidelectrolyte material’.

A lithium battery of the present invention is hereinafter described ineach constitution.

1. Solid Electrolyte Layer

A solid electrolyte layer in the present invention is first described. Asolid electrolyte layer in the present invention contains theabove-mentioned solid electrolyte material. The range of the thicknessof the solid electrolyte layer is preferably the same as the range ofthe thickness of the above-mentioned solid electrolyte material.

2. Cathode Active Material Layer

Next, a cathode active material layer in the present invention isdescribed. A cathode active material layer in the present invention is alayer containing at least a cathode active material, and may contain atleast one of a conductive material, a solid electrolyte material and abinder, as required. Examples of the cathode active material includeLiCoO₂, LiMnO₂, Li₂NiMn₃O₈, LiVO₂, LiCrO₂, LiFePO₄, LiCoPO₄, LiNiO₂ andLiNi_(1/3)CO_(1/3)Mn_(1/3)O₂.

A cathode active material layer in the present invention may furthercontain a conductive material. The addition of the conductive materialallows the conductivity of the cathode active material layer to beimproved. Examples of the conductive material include acetylene black,Ketjen Black and carbon fiber. Further, the cathode active materiallayer may further contain a solid electrolyte material. The addition ofthe solid electrolyte material allows Li ion conductivity of the cathodeactive material layer to be improved. Examples of the solid electrolytematerial include an oxide solid electrolyte material and a sulfide solidelectrolyte material. Further, the cathode active material layer mayfurther contain a binder. Examples of the binder include afluorine-containing binder such as polytetrafluoroethylene (PTFE). Thethickness of the cathode active material layer is preferably within arange of 0.1 μm to 1000 μm, for example.

3. Anode Active Material Layer

Next, an anode active material layer in the present invention isdescribed. An anode active material layer in the present invention is alayer containing at least an anode active material, and may contain atleast one of a conductive material, a solid electrolyte material and abinder, as required. Examples of the anode active material include ametal active material and a carbon active material. Examples of themetal active material include In, Al, Si, and Sn. On the other hand,examples of the carbon active material include mesocarbon microbeads(MCMB), high orientation property graphite (HOPG), hard carbon and softcarbon.

A conductive material, a solid electrolyte material and a binder usedfor the anode active material layer are the same as in the case of theabove-mentioned cathode active material layer. The thickness of theanode active material layer is preferably within a range of 0.1 μm to1000 μm, for example.

4. Other Constitutions

A lithium battery of the present invention comprises at least theabove-mentioned solid electrolyte layer, cathode active material layerand anode active material layer, ordinarily further comprising a cathodecurrent collector for performing current collecting of the cathodeactive material layer and an anode current collector for performingcurrent collecting of the anode active material layer. Examples of amaterial for the cathode current collector include SUS, aluminum,nickel, iron, titanium and carbon, and preferably SUS among them. On theother hand, examples of a material for the anode current collectorinclude SUS, copper, nickel and carbon, and preferably SUS among them.Factors such as the thickness and shape of the cathode current collectorand the anode current collector are preferably selected properlydepending on the uses of a lithium battery. A battery case of a generallithium battery may be used for a battery case used for the presentinvention. Examples of the battery case include a battery case made ofSUS.

5. Lithium Battery

A lithium battery of the present invention may be a primary battery or asecondary battery, and preferably a secondary battery among them. Thereason therefor is to be repeatedly chargeable and dischargeable and beuseful as a car-mounted battery, for example. Examples of the shape of alithium battery of the present invention include a coin shape, alaminate shape, a cylindrical shape and a rectangular shape. A method ofproducing a lithium battery of the present invention is not particularlylimited as long as it is a method for allowing the above-mentionedlithium battery, and the same method as that of producing a generallithium battery may be used. Examples thereof include a method such thata material constituting a cathode active material layer, a materialconstituting a solid electrolyte layer and a material constituting ananode active material layer are sequentially pressed to thereby producea power generating element and this power generating element is storedinside a battery case, which is crimped.

C. Method of Producing Solid Electrolyte Material

Next, a method of producing a solid electrolyte material of the presentinvention is described. A method of producing a solid electrolytematerial of the present invention comprises steps of: preparing a rawmaterial, in which the raw material is constituted of Li, La, Ti, M1 (M1being at least one selected from the group consisting of Sr, Na, Nd, Pr,Sm, Gd, Dy, Y, Eu, Tb, and Ba), and M2 (M2 being at least one selectedfrom the group consisting of Mg, W, Mn, Al, Ge, Ru, Nb, Ta, Co, Zr, Hf,Fe, Cr, and Ga); and forming a thin film, in which the solid electrolytematerial is formed using the raw material to a substrate by a reactivedeposition method using oxygen, and the solid electrolyte material isrepresented by a general formula:Li_(x)(La_(2−a)M1_(a))(Ti_(3−b)M2_(b))O_(9+δ), in which “x” is 0<x≦1;“a” is 0≦a≦2; “b” is 0≦b≦3; and “δ” is −2≦δ≦2.

According to the present invention, the use of the reactive depositionmethod allows a minute thin film to be formed, and a solid electrolytematerial having excellent Li ion conductivity may be obtained by theabove-mentioned general formula.

FIG. 3 is a schematic cross-sectional view showing an example of amethod of producing a solid electrolyte material of the presentinvention. In FIG. 3, a crucible 12 in which Li metal, La metal and Timetal are put, and a substrate 13 are first placed in a chamber 11.Next, the pressure of the chamber 11 is reduced to form a vacuum state.Thereafter, O₂ plasma is caused to simultaneously volatilize Li metal,La metal and Ti metal by a resistance heating method and an electronbeam method. Thus, an LiLaTiO thin film 14 is deposited on the substrate13. A thin film with high amorphous nature is obtained if the substrateis not heated during the deposition, and a thin film with highcrystallinity is obtained by heating the substrate during the depositionor post-heating a thin film deposited on the substrate.

A method of producing a solid electrolyte material of the presentinvention is hereinafter described at each step.

1. Step of Preparing Raw Material

The step of preparing a raw material in the present invention is firstdescribed. Step of preparing a raw material in the present invention isa step of preparing a raw material, in which the raw material is made ofLi, La, Ti, M1 (M1 being at least one selected from the group consistingof Sr, Na, Nd, Pr, Sm, Gd, Dy, Y, Eu, Tb, and Ba), and M2 (M2 being atleast one selected from the group consisting of Mg, W, Mn, Al, Ge, Ru,Nb, Ta, Co, Zr, Hf, Fe, Cr, and Ga).

In the present invention, simplex metals of Li, La, Ti, M1 and M2 areordinarily prepared. These simplex metals have preferably high purity.The reason therefor is to allow a solid electrolyte material with fewerimpurities. Further, ordinarily, M1 is not used in the case of obtaininga solid electrolyte material in which “a” in the above-mentioned generalformula is 0, and M2 is not used in the case of obtaining a solidelectrolyte material in which “b” in the above-mentioned general formulais 0.

2. Step of Forming Thin Film

Next, the step of forming a thin film in the present invention isdescribed. The step of forming a thin film in the present invention is astep of forming the above-mentioned solid electrolyte material whileusing the above-mentioned raw material to a substrate by a reactivedeposition method using oxygen.

In the present invention, the solid electrolyte material is formed by areactive deposition method. In this method, the thin-film solidelectrolyte material is formed by volatilizing the raw material to reactthe volatilized raw material with oxygen. Examples of a method ofvolatilizing the raw material include a resistance heating method and anelectron beam method. Examples of a method of reacting the volatilizedraw material with oxygen include a method of using oxygen plasma and amethod of using oxygen gas. In addition, in the present invention, thereactive deposition is preferably performed in vacuo, and is preferablyperformed specifically in a vacuum of 1×10⁻¹⁰ mBar or less. The reasontherefor is that a minute thin film may be formed. The thickness of thesolid electrolyte material may be controlled by deposition time.

Further, in the present invention, the thin-film solid electrolytematerial is formed on the substrate. The substrate in the presentinvention is not particularly limited and preferably selected properlydepending on the uses of the solid electrolyte material. For example, inthe case of using the solid electrolyte material as a solid electrolytelayer of a lithium battery, a member having a cathode active materiallayer or an anode active material layer is preferably used as thesubstrate.

Further, in the present invention, the heating of the thin film formedon a substrate allows the solid electrolyte material with highcrystallinity to be formed. Heating temperature is preferably atemperature of the crystallizing temperature or more of a crystal phaserepresented by the above-mentioned general formula; for example, withina range of 600° C. to 800° C. Heating time is preferably within a rangeof 0.5 hour to 3 hours, for example. Further, examples of a method ofpost-heating the thin film include a method by using a baking furnace,for example. In addition, an atmosphere for heating the thin film may bean air atmosphere or an inert gas atmosphere.

3. Others

A solid electrolyte material obtained by the present invention is thesame content as that described in the above-mentioned ‘A. Solidelectrolyte material’; therefore, the description herein is omitted. Thepresent invention may provide a solid electrolyte material characterizedby being obtained by the above-mentioned method of producing a solidelectrolyte material.

The present invention is not limited to the above-mentioned embodiments.The above-mentioned embodiments are exemplification, and any one thathas substantially the same constitution as that of the technical ideadescribed in the claim of the present invention and exerts similareffect is included in the technical scope of the present invention.

EXAMPLES

The present invention is described more specifically while showingExamples hereinafter.

Example 1

Lithium metal (ribbon, a purity of 99.9%, manufactured by Sigma-AldrichCo. LLC.), lanthanum metal (a purity of 99.9%, manufactured bySigma-Aldrich Co. LLC.), and titanium metal (slug, a purity of 99.98%,manufactured by Alfa Aesar) were first prepared as a raw material. Next,the lithium metal was put in a 40-cm³ crucible made of pyrolytic boronnitride (PBN) and placed in a chamber. Next, the lanthanum metal and thetitanium metal were each put in a 40-cm³ crucible made of pyrolyticgraphite and placed in the chamber in the same manner. An Si/SiO₂/Ti/Ptlaminated body (manufactured by NOVA Electronic Materials, LLC.) wasused as a substrate, a deposition area was determined at 0.785 cm²(equivalent to φ 10 mm), and a distance from the raw material to thesubstrate was determined at 500 mm. Next, the inside of the chamber wassubject to a high vacuum of 1×10⁻¹⁰ mBar or less.

Thereafter, resistance heating (Knudsen Cells) was performed for thecrucible in which the lithium metal was put to volatilize the lithium,and simultaneously electron beam irradiation was performed for thecrucible in which the lanthanum metal was put and the crucible in whichthe titanium metal was put to volatilize the lanthanum metal and thetitanium metal. Oxygen plasma was caused in the chamber by using anoxygen plasma generator (manufactured by Oxford Applied Research Ltd.,RF source, HD25) and reacted with the volatilized raw material tothereby obtain a thin-film solid electrolyte material on the substrate.The substrate was heated to a temperature of 700° C. during thedeposition.

The thickness of the obtained solid electrolyte material was 410 nm.When XRD measurement (using CuKα) was performed for the obtained solidelectrolyte material, it was confirmed that the solid electrolytematerial was a crystalline material and had a perovskite structure. WhenICP analysis (inductively coupled plasma analysis) was performed for theobtained solid electrolyte material, a result of Li:La:Ti=0.02:2:3 wasobtained and it was confirmed that the composition of the obtained solidelectrolyte material was Li_(0.02)La₂Ti₃O_(9+δ) (x=0.02).

Examples 2 to 7

A thin-film solid electrolyte material was obtained in the same manneras in Example 1 except for properly adjusting the amount of the metalsvolatilized from the crucible with a shutter. The composition of thesolid electrolyte material obtained in Examples 2 to 7 wasLi_(0.9)La₂Ti₃O_(9+δ) (x=0.09), Li_(0.10)La₂Ti₃O_(9+δ) (x=0.10),Li_(0.11)La₂Ti₃O_(9+δ) (x=0.11) Li_(0.16)La₂Ti₃O_(9+δ) (x=0.16),Li_(0.24)La₂Ti₃O_(9+δ) (x=0.24) and Li_(0.28)La₂Ti₃O_(9+δ) (x=0.28),respectively.

[Evaluation 1]

Activation energy of Li ion conduction in each of the solid electrolytematerial obtained in Examples 1 to 7 was evaluated. Platinum was firstdeposited on the surface of the solid electrolyte material formed on thesubstrate to produce a symmetrical cell of Pt/solid electrolytematerial/Pt. Next, an alternating current impedance method was performedat temperatures of 200 K, 250 K, 300 K, 350 K, 400 K, 450 K and 500 K tocalculate activation energy of Li ion conduction. The result is shown inTable 1 and FIG. 4.

TABLE 1 ACTIVATION CHEMICAL FORMULAE ENERGY EXAMPLE 1Li_(0.02)La₂Ti₃O_(9+δ) (x = 0.02) 0.58 eV EXAMPLE 2Li_(0.09)La₂Ti₃O_(9+δ) (x = 0.09) 0.54 eV EXAMPLE 3Li_(0.10)La₂Ti₃O_(9+δ) (x = 0.10) 0.54 eV EXAMPLE 4Li_(0.11)La₂Ti₃O_(9+δ) (x = 0.11) 0.53 eV EXAMPLE 5Li_(0.16)La₂Ti₃O_(9+δ) (x = 0.16) 0.47 eV EXAMPLE 6Li_(0.24)La₂Ti₃O_(9+δ) (x = 0.24) 0.53 eV EXAMPLE 7Li_(0.28)La₂Ti₃O_(9+δ) (x = 0.28) 0.60 eV

As shown in Table 1 and FIG. 4, the activation energy became 0.60 eV orless in Examples 1 to 7. In particular, when “x” became 0.09 or more,the activation energy decreased remarkably and minimized at x=0.16. Inaddition, it was confirmed that Example 6 also gave as low activationenergy as Examples 2 to 4. As described above, it was confirmed that asolid electrolyte material of the present invention exhibited excellentLi ion conductivity for the reason that smaller activation energy Ebrought larger Li ion conductivity σ.

Reference Example 1

A thin-film solid electrolyte material was obtained in the same manneras in Example 1 except for properly adjusting the amount of the metalsvolatilized from the crucible with a shutter. The composition of thesolid electrolyte material obtained in Reference Example 1 wasLi_(0.42)La_(0.58)TiO₃. This composition is included in a compositionarea described in Patent Literature 1, and differs from the compositionin the present invention. Further, the difference is that the solidelectrolyte material described in Patent Literature 1 is amorphous whilethe solid electrolyte material obtained in Reference Example 1 is acrystalline material.

Reference Example 2

A thin-film solid electrolyte material was obtained in the same manneras Example 1 except for properly adjusting the amount of the metalsvolatilized from the crucible with a shutter. The composition of thesolid electrolyte material obtained in Reference Example 2 wasLi_(0.09)La_(0.64)TiO₃. This composition is included in a compositionarea described in Patent Literature 2, and differs from the compositionin the present invention. Further, the difference is that the solidelectrolyte material described in Patent Literature 2 is a bulk bodywhile the solid electrolyte material obtained in Reference Example 2 isin thin film form.

[Evaluation 2]

Activation energy of Li ion conduction in the solid electrolytematerials obtained in Reference Examples 1 and 2 was evaluated. Theevaluation method is the same as the above. The result is shown in Table2.

TABLE 2 CHEMICAL ACTIVATION FORMULAE ENERGY REFERENCE EXAMPLE 1Li_(0.42)La_(0.58)TiO₃ 0.61 eV REFERENCE EXAMPLE 2Li_(0.09)La_(0.64)TiO₃ 0.62 eV

As shown in Table 2, the activation energy became more than 0.60 eV inReference Examples 1 and 2. Further, in particular, it was confirmedthat the activation energy was lower in Examples 2 to 6 when ReferenceExamples 1 and 2 were compared with Examples 2 to 6.

REFERENCE SIGNS LIST

1 . . . cathode active material layer

2 . . . anode active material layer

3 . . . solid electrolyte layer

4 . . . cathode current collector

5 . . . anode current collector

6 . . . battery case

10 . . . lithium battery

11 . . . chamber

12 . . . crucible

13 . . . substrate

14 . . . LiLaTiO thin film

The invention claimed is:
 1. A solid electrolyte material represented bya general formula: Li_(x)(La_(2−a)M1_(a))(Ti_(3−b)M2_(b))O_(9+δ),wherein “x” is 0.02≦x≦0.28; “a” is 0≦a≦2; “b” is 0≦b≦3; “δ” is −2≦δ≦2;“M1” is at least one selected from the group consisting of Sr, Na, Nd,Pr, Sm, Gd, Dy, Y, Eu, Tb, and Ba; and “M2” is at least one selectedfrom the group consisting of Mg, W, Mn, Al, Ge, Ru, Nb, Ta, Co, Zr, Hf,Fe, Cr, and Ga.
 2. The solid electrolyte material according to claim 1,wherein the “x” is 0.09≦x≦0.24.
 3. The solid electrolyte materialaccording to claim 1, wherein the solid electrolyte material is acrystalline material.
 4. The solid electrolyte material according toclaim 1, wherein the solid electrolyte material has a perovskitestructure.
 5. The solid electrolyte material according to claim 1,wherein the solid electrolyte material is in thin film form.
 6. Thesolid electrolyte material according to claim 1, wherein the solidelectrolyte material has a thickness of 200 nm to 5 μm.
 7. The solidelectrolyte material according to claim 1, wherein the “a” and the “b”are
 0. 8. A lithium battery comprising: a cathode active material layercontaining a cathode active material, an anode active material layercontaining an anode active material, and a solid electrolyte layerformed between the cathode active material layer and the anode activematerial layer, wherein the solid electrolyte layer contains the solidelectrolyte material of claim
 1. 9. A method of producing a solidelectrolyte material comprising steps of: preparing a raw material, inwhich the raw material is made of Li, La, Ti, M1(M1 being at least oneselected from the group consisting of Sr, Na, Nd, Pr, Sm, Gd, Dy, Y, Eu,Tb, and Ba), and M2 (M2 being at least one selected from the groupconsisting of Mg, W, Mn, Al, Ge, Ru, Nb, Ta, Co, Zr, Hf, Fe, Cr, andGa); and forming a thin film, in which a solid electrolyte material isformed using the raw material to a substrate by a reactive depositionmethod using an oxygen, and the solid electrolyte material isrepresented by a general formula:Li_(x)(La_(2−a)M1_(a))(Ti_(3−b)M2_(b))O_(9+δ), “x” being 0.02≦x≦0.28 and“a” being 0≦a≦2, “b” is 0≦b≦3, and “δ” is −2≦δ≦2.
 10. The method ofproducing a solid electrolyte material according to claim 9, wherein thesolid electrolyte material is a crystalline material and has aperovskite structure.
 11. The method of producing a solid electrolytematerial according to claim 9, wherein the solid electrolyte materialhas a thickness of 200 mn to 5 μm.
 12. The method of producing a solidelectrolyte material according to claim 9, wherein the solid electrolytematerial is formed in the thin film forming step by the reactivedeposition method using an oxygen plasma.
 13. The method of producing asolid electrolyte material according to claim 9, wherein the substrateis a member containing a cathode active material layer or an anodeactive material layer.